Storage system and method for controlling the same

ABSTRACT

Optimum load distribution processing is selected and executed based on settings made by a user in consideration of load changes caused by load distribution in a plurality of asymmetric cores, by using: a controller having a plurality of cores, and configured to extract, for each LU, a pattern showing the relationship between a core having an LU ownership and a candidate core as an LU ownership change destination based on LU ownership management information; to measure, for each LU, the usage of a plurality of resources; to predicate, for each LU based on the measurement results, a change in the usage of the plurality of resources and overhead to be generated by transfer processing itself; to select, based on the respective prediction results, a pattern that matches the user&#39;s setting information; and to transfer the LU ownership to the core belonging to the selected pattern.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of Ser. No. 13/407,995,filed Feb. 29, 2012, which is a continuation application of applicationSer. No. 12/444,036, filed Apr. 2, 2009, now U.S. Pat. No. 8,146,092,issued Mar. 27, 2012 the disclosure of which is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates generally to a storage system. Moreparticularly, this invention relates to a technique for improving theperformance of a storage system constituted from a plurality ofresources including microprocessors.

BACKGROUND ART

A storage system is constituted from: a storage control unit forexecuting processing of data issued by a host computer; and storagedevices for storing data. A technique for improving the reliability ofthe storage system by providing a plurality of storage control unitsdescribed above and realizing data redundancy in storage devices isknown (Japanese Patent Application Laid-Open (Kokai) Publication No.2008-134775).

Japanese Patent Application Laid-Open (Kokai) Publication No.2008-134775 discloses a storage system having a plurality of storagecontrol units, wherein load is distributed by using a technique fordelivering an input/output request issued by a host computer to aprocessor that should process the input/output request, therebyimproving a data processing speed.

RELATED ART DOCUMENT

-   [Patent Document 1] Japanese Patent Application Laid-Open (Kokai)    Publication No. 2008-134775

DISCLOSURE OF THE INVENTION

The above-mentioned publication discloses a system having a plurality ofcores in a storage control unit. In this case, different resources areused for data processing between the cores in the same storage controlunits and between the cores in different storage control units.Therefore, as a result of load distribution, the processor cores may beuniformly loaded, but other resources may be ununiformly loaded.

Furthermore, overhead is generated when logical units which theprocessor core takes charge of are switched for the purpose of loaddistribution. Therefore, switching the logical units only for thepurpose of load distribution may possibly degrade the performance of thestorage system.

It is an object of the present invention to provide: a storage systemcapable of selecting and executing optimum load distribution processingbased on the user's settings in consideration of load changes caused byload distribution in a plurality of asymmetric cores; and a method forcontrolling such a storage system.

In order to achieve the above-described object according to an aspect ofthe present invention, a plurality of asymmetric cores are provided ascores that receive an LU ownership in processing objects and therebytake charge of processing of the processing objects; and whendistributing the load on the respective cores, patterns showing therelationship between a core having the LU ownership and a candidate coreas a destination of transfer of the LU ownership are extracted for eachprocessing object; the usage of the respective resources constitutingthe storage system is acquired; the state changes that may occur inassociation with the load distribution in each core are predicted basedon the acquired usage of the respective resources; a pattern thatmatches the set conditions is selected based on the prediction results;and the LU ownership change destination is decided in accordance withthe selected pattern.

EFFECT OF THE INVENTION

According to the present invention, optimum load distribution in aplurality of asymmetric cores can be performed in accordance withsettings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a storage system according to an embodimentof the present invention.

FIG. 2 is a memory configuration diagram of the storage system accordingto the embodiment of the present invention.

FIG. 3 is a cache memory configuration diagram of the storage systemaccording to the embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating configuration informationof the storage system according to the embodiment of the presentinvention.

FIG. 5 is a configuration diagram illustrating performance informationof the storage system according to the embodiment of the presentinvention.

FIG. 6 is a configuration diagram illustrating resource usage managementinformation of the storage system according to the embodiment of thepresent invention.

FIG. 7 is a configuration diagram illustrating information aboutprediction results of changes in the resource usage after transfer ofthe LU ownership in the storage system according to the embodiment ofthe present invention.

FIG. 8 is a configuration diagram illustrating information aboutprediction results of overhead to be generated by LU ownership changeprocessing itself executed by the storage system according to theembodiment of the present invention.

FIG. 9 is a flowchart illustrating balancing processing executed by thestorage system according to the embodiment of the present invention.

FIG. 10 is a flowchart illustrating simplified balancing processingexecuted by the storage system according to the embodiment of thepresent invention.

FIG. 11 is a flowchart illustrating normal balancing processing executedby the storage system according to the embodiment of the presentinvention.

FIG. 12 is a management screen configuration diagram for explaining howa user of the storage system makes settings according to the embodimentof the present invention.

FIG. 13 is another form of management information configuration diagramshowing the resource usage of the storage system according to theembodiment of the present invention.

FIG. 14 is a flowchart illustrating performance information acquisitionand analysis processing executed by the storage system according to theembodiment of the present invention.

FIG. 15 is a configuration diagram of a performance information displayscreen for the user of the storage system according to the embodiment ofthe present invention.

FIG. 16 is a configuration diagram of an LU ownership change processinghistory display screen for the user of the storage system according tothe embodiment of the present invention.

FIG. 17 is a configuration diagram of an automatic setting managementscreen for the user of the storage system according to the embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be explained below withreference to the attached embodiment. FIG. 1 is a configuration diagramof a storage system according to an embodiment of the present invention.Referring to FIG. 1, the storage system includes a storage system 101,host computers 103, 104, and management host 105.

Each host computer 103, 104 has a communication port (not shown) forconnection to the storage system 101, and is thereby connected via thiscommunication port and a connection path 184, 185 to the storage system101. The management host 105 is connected to the storage system 101 viaa management connection path 183. The management host 105 is configuredas an input unit for a user to input setting information such as settinginformation as a policy of load distribution.

FIG. 1 shows a configuration in which the host computers 103, 104, themanagement host 105, and the storage system 101 are directly connectedto each other. A network called “SAN (Storage Area Network)” may be usedfor connection to the host, and a network called “LAN (Local AreaNetwork)” may be used for connection to the management host, and aconfiguration that enables connection to many host computers andmanagement hosts may be used. Protocols such as Fibre Channel and iSCSI(Small Computer System Interface over Internet) can be used as the SAN.Furthermore, the same connection path as that for connection to the hostcan be used for connection to the management host.

The storage system 101 contains a controller 111, a controller 151, anddisks 181. The controllers 111, 151 are given numbers “0” and “1”respectively, as “controller numbers.” The controllers 111 and 151 areconnected via an inter-controller bus 182. The controllers 111, 151 andthe disks 181 are connected via disk connection paths 121, 161.

Referring to FIG. 1, the disks 181 are used as general storage devices.For example, HDDs (Hard Disk Drives) for FC (Fibre Channel), SAS (SANAttached Storage), ATA (AT Attachment), or SSD (Solid State Drive) maybe used as the disks 181. Moreover, storage media, other than disks 181,such as tapes or flash memories may be used. Furthermore, a RAID(Redundant Array of Inexpensive Disks) may be configured using a singledisk 181 and a plurality of disks 181, and the disks 181 having the RAIDconfiguration can be access objects of the host computers 103, 104.

The controller 111 includes a host input/output controller unit 119, adata transfer control unit 112, a disk input/output controller unit 118,a cache memory 117, a management I/F115, a CPU (Central Processing Unit)114, a bridge 113, and a memory 116.

The management I/F 115 is connected via an internal bus 136 to thebridge. The management I/F 115 is also connected via the managementconnection path 183 to the management host 105 and controls datatransmission/reception to/from the management host 105 andcommunications with the management host 105.

The memory 116 is connected via an internal bus 134 to the bridge 113.The CPU 114 is connected via an internal bus 135 to the bridge 113 andstores a plurality of cores 122.

FIG. 1 shows the CPU 114 as a single component, but the storage systemmay be provided with a plurality of CPUs 114. Regarding how to use theplurality of cores or processors, there are a symmetric processingmethod called “SMP (Symmetric Multi Processing)” and an asymmetricprocessing method called “AMP (Asymmetric Multi Processing).”

By the SMP method, an OS (Operating System) generally decides which coreor processor should execute which processing. In this case, the effectof load distribution varies greatly depending on which core or processoractually executes the processing. Therefore, control programs includingthe OS are required to be capable of selecting the core or processor forexecuting the processing.

By the AMP method, the control programs can expressly designate the coreor processor for executing the processing. In the case of the SMPmethod, the OS has the function capable of selecting the core orprocessor for executing the processing; and, therefore, this function isutilized. Incidentally, in the case of the AMP method, there is animplementation method in which each core processor takes charge ofspecific processing and all the processing cannot be executed by onlyone core processor.

If the setting is made so that only the 0^(th) core can control the hostinput/output control unit 119, processing for input/output to/from thestorage system 101 cannot be executed without using this core.

Unless specifically noted, the term “core” used hereinafter means aprocessing system capable of processing all inputs/outputs to/from thestorage system 101. In other words, the core 122 executes variousarithmetic processing in accordance with programs stored in the memory116 and controls the entire controller 111 based on the processingresults.

The data transfer control unit 112 is connected via an internal bus 137to the bridge 113. The data control unit 112 controls data transfer inthe controller 111. Also, the data transfer control unit 112 and thedata transfer control unit 152 are connected to each other via theinter-controller bus 182. As a result, the controllers 111, 151 cancommunicate with each other via the inter-controller bus 182.

The cache memory 117 is connected via an internal bus 133 to the datatransfer control unit 112 and temporarily stores data to be transferredwhen transferring the data.

The host input/output control unit 119 is connected via the connectionpath 184 to the host computer 103 and controls input/output from/to thehost computer 103.

The disk input/output control unit 118 is connected via the diskconnection path 121 to the disks 181 and controls data input/output fromand to the disks.

The controller 151, like the controller 111, includes a hostinput/output control unit 159, a data transfer control unit 152, a diskinput/output control unit 158, a cache memory 157, a management I/F155,a CPU 154, a bridge 153, and a memory 156; and the CPU 154 isconstituted from a plurality of cores 162.

The respective components shown in this embodiment are not necessarilyessential. For example, there is a configuration where a chip in whichthe CPU 114 and the bridge 113 are integrated may be used, or a chip inwhich the CPU 114, the bridge 113, and the data transfer control unit112 are integrated may be used. Furthermore, there are a configurationwhere the cache memory 117 and the memory 116 are realized by the samememory, and a configuration constituted from a plurality of processorsdescribed above.

If the components are changed as described above, the content ofresource usage management information 501 described later will changeaccording to the configuration. If the configuration is changed so thatthe memory 116 includes the cache memory 117, the bus 133 for connectingthe cache memory 117 and the data transfer control unit 112 does notexist and, instead, data corresponding to the data to be suppliedbetween the cache memory 117 and the data transfer control unit 112 willbe supplied to the internal bus 134.

Also, there is a configuration that uses physically different memoriesbetween processors in a multiprocessor environment. In this case, it isnecessary to measure and evaluate the resource usage of the memories andthe memory busses individually. As a matter of course, it is possible torealize the configuration similar to that described above, even in amulti-core configuration. In this case, the above-mentioned individualevaluation is required.

The memory 116, as shown in FIG. 2, stores a common memory area forcores in a controller 201, a common memory area for controllers 202, andan exclusive core area 203. Information stored in each of these areaswill be described below. However, all these pieces of information arenot always required to be stored in the areas shown in FIG. 2.

If control information 231 is stored in the common area for cores in acontroller 201, the used memory size will be reduced. On the other hand,if the control information 231 is stored in the exclusive core area 203,the memory size will increase due to redundancy of the controlinformation 231 and an increase of useless areas, but storing thecontrol information 231 in the exclusive core area 203 has the effect ofimproving the performance by, for example, elimination of the necessityto execute exclusive processing when accessing inter-core information.

The exclusive core area 203 stores the control information 231. Thecontrol information 231 is information needed when the cores 122 for theCPU114 process I/O issued to the storage system 111. The controlinformation 231 includes, for example, memory information managed by thecores 122 as well as information tables to which the host input/outputcontrol unit 119 and the disk input/output control unit 118 refer. Theexclusive core area 203 basically stores only the information necessaryfor the areas which the cores 122, 162 are in charge of.

As the areas which the cores 122, 162 are in charge of, LU (LogicalUnits) that are processing objects of the cores 122, 162 are hereinafterconsidered to be units which the cores 122, 162 are in charge of. Alogical unit LU is a virtual logical area configured in physical storageareas of the disks 181. As a matter of course, a range different fromthat of the LU can be the range which the cores 122, 162 are in chargeof.

The common memory area for controllers 202 stores configurationinformation 221 and performance information 222.

The common area for cores in a controller 201 stores an operating system211, a disk array control program 212, a data transfer control unitcontrol program 213, an input/output control unit control program 214, aperformance information measurement program 215, a performanceinformation analysis program 218, and an LU ownership change program217. Each program is executed by each core 122, 162. The followingexplanation is given on that condition.

The LU ownership change program 217 is a program that performs operationon LUs, which each core is in charge of, to transfer the LU ownership inone core to another core. The performance information measurementprogram 215 is a program for monitoring the usage of various resourcesin the storage system 101, measuring to what degree each resource isbeing used, and storing the measurement results in the performanceinformation 222. The performance information analysis program 216 is aprogram for analyzing the performance information 222 measured by theperformance information measurement program 215 and controlling theexecution of LU ownership change processing.

The data transfer control unit control program 213 is a program forcontrolling the data transfer control unit 112, and the input/outputcontrol unit control program 214 is a program for controlling the hostinput/output control unit 119 and the disk input/output control unit118. The operating system 211 is a program used for the operation of thecores for the CPU 114, and the disk array control program 212 is aprogram used for controlling the entire disk array by performing, forexample, calculation of the address of input/output to/from the disks181.

The memory 156 has a configuration similar to that of the memory 116.The LU ownership change program 217 is a program for changing the corein charge of processing of an input/output request received from thehost computer 103, 104, but not limiting a physical port to receive aninput/output request. In other words, processing of an input/outputrequest received from the host computer 103, 104 prior to the LUownership change processing will not be disabled by the LU ownershipchange processing, and the transfer processing can be executed withoutstopping the input/output request.

The cache memory 117, as shown in FIG. 3, stores a local controller area301 and an external controller area 341. The local controller area 301means an area used by the cores for the controller in which the relevantcache memory exists. For example, in the cache memory 117 in thecontroller 111 with controller number “0,” the local controller area 301is an area used by the cores 122 for the controller 111.

The external controller area 341 means an area used by the cores forcontrollers other than the controller in which the relevant cache memoryexists. For example, in the cache memory 117, the external controllerarea 341 is an area used by the cores 157 for the controller 151. In thecache memory 157 for the controller 151, the local controller area andthe external controller area are opposite to those for the cache memory117 for the controller 111.

The local controller area 301 stores local controller managementinformation 311 and local controller data 312. The local controllermanagement information 311 is management information used by the coresfor the controller 111, such as the storage status of the localcontroller data 312. The external controller area 341 stores externalcontroller management information 351 and external controller data 352.

In this way, fault tolerance is improved also for data used by theexternal controller by storing it in the cache memory 117.

From among the above-mentioned pieces of information, the controllermanagement information 311, 351 is mirror-written by the cores 122, 162,and the controller data 312, 352 is mirror-written mainly by the datatransfer control units 112, 152. As a result, the cache memories 117,157 store both the controller management information 311, 351 and thecontroller data 312, 352.

As a matter of course, there is some information that is only requiredto be stored in the local controller in order to reduce the load.Therefore, the above-mentioned pieces of information are not necessarilycompletely dualized. If the cache memory 117 is used as a temporary areafor operation, it is only necessary to temporarily store data only inthe local controller area 301, and the local controller area 301 may notnecessarily completely correspond to the external controller area in thecache memory 157.

The configuration information 221, as shown in FIG. 4, is constitutedfrom LU ownership management information 401, balancing parameterinformation 402, and data storage information 403.

The LU ownership management information 401 stores an LU ownershipmanagement table T401 that manages a correspondence relationshipindicating which core is in charge of I/O to/from each area. Since theLU is the management area unit in this embodiment, FIG. 4 shows themanagement of which core is currently in charge of processing withregard to each LU.

The balancing parameter information 402 stores a balancing parametertable T402. The balancing parameter table T402 includes defaultparameters or parameters set by the user as parameters used whenexecuting load balancing, and provides guidelines for determining thedetails of processing when controlling the load balance. To what degreethe load balancing should be performed is decided based on a numericvalue set as a load balance priority and a numeric value set as astorage system performance priority.

If the load balance priority is high and the storage system performancepriority is low, the load balance is controlled so that the load on therespective resources will be distributed and balanced, even though thesystem performance might slightly degrade. Conversely, if the loadbalance priority is low and the storage performance priority is high,the load balance is controlled so that the total performance will beenhanced, even though the load may be slightly imbalanced.

An acceptable transfer overhead level is a parameter indicating to whatdegree the overhead generated by operation of the aforementioned LUownership change program 217 and execution of the LU ownership changeprocessing is acceptable. If this numeric value is low, i.e., if theacceptable level is low, only transfer with small overhead is permitted.This means that transfer with a small amount of information to take overas a result of the transfer is permitted, for example, in a case whereI/O has been stopped for a certain period of time prior to the transferand no or only little data exists in the cache memory 117, 157.

A performance information reference range is the range of performanceinformation to which reference is made when transferring the LUownership. If a short period of time is set to this parameter, loadchanges in the short period of time can be followed, but the possibilityof executing the LU ownership change which is essentially unnecessary orharmful in terms of performance may increase due to a temporary orsudden load change. Conversely, if a long period of time is set to thisparameter, the probability of failure in transferring the LU ownershipwill decrease, but the possibility of not transferring the LU ownershipor delaying the transfer time will increase in the situation where theLU ownership change should be executed.

An assignment priority is set when the user expressly indicates the LUownership and does not intend to transfer the LU ownership. In otherwords, the assignment priority is used for the purpose of, for example,performance assurance in a case where the LU ownership in a certain LUis set to a specific core and no transfer of the LU ownership from thiscore is permitted, and transfer of an LU ownership in another LU to thecore specified above is not permitted.

The data storage information 403 is constituted from a data storageinformation table T403. The data storage information table T403 isinformation indicating where to store data issued to the LUs managed bythe storage system 101, and stores information necessary for datastorage processing.

The performance information 222 stores, as shown in FIG. 5, resourceusage management information 501, post-LU-ownership-change resourceusage change prediction information 502, and LU ownership changeprocessing overhead prediction information 503.

The resource usage management information 501 stores a resource usagemanagement information table T601 as shown in FIG. 6. The resource usagemanagement information table T601 stores the usage of each resource asmeasured for each LU, which is the LU ownership management unit, by theperformance information measurement program 215, together with the pasthistory. Whether or not the load is imbalanced in the current storagesystem 101 can be judged based on the resource usage managementinformation table T601. Also, information about whether the load remainsimbalanced or not and what degree of change has occurred can be acquiredbased on the past history.

Incidentally, as shown in the resource usage management informationtable T601, the load with regard to a certain LU is not necessarilyimposed on the core in charge of that LU and the controller thereof.This is because the inter-controller bus 182 and the buses 133, 173 forconnecting the cache memories 117, 157 and the data transfer controlunits 11, 152 are used to utilize these resources, for example, whendata is stored in the cache memory for the external controller bymirror-writing of the data.

Furthermore, the resource usage management information 501 shows all theusage of the resources as measured by the performance informationmeasurement program 215 in relation to the performance of the storagesystem 101 and contains many pieces of information other than theabove-described items.

Particularly, the usage of the cache memories 117 and 157 stored inresource usage management information 1301 and a resource usagemanagement information table T1301 shown in FIG. 13 have a significantinfluence on the performance in the LU ownership change processing.Dirty data from among data existing in the cache memory 117 representsdata that has not been reflected in the disks 181; and if there is alarge amount of dirty data, it means that many processing sequences areleft uncompleted for the relevant LU. Therefore, there is a possibilitythat the LU having a large amount of dirty data may temporarily imposelarge load, in addition to I/O load at that time, on the processor towhich the LU ownership has been transferred; and, as a result, it ispossible to consider/predict the possibility of the temporary impositionof large load by referring to the dirty data recorded in this tableT1301.

Besides the dirty data, the amount of data that is not mirror-writtenalso has an influence on the performance in the LU ownership changeprocessing. Generally, dirty data is often mirror-written to the cachememories 117 and 157 in preparation for failures such as electric powerinterruption.

On the other hand, non-dirty data and dirty data of low importance aresometimes not mirror-written for the purpose of reduction of the usagerate of the inter-controller bus 182 and the usage of the cache.Regarding the mirror-written data, the same data already exists in thecache memories 117 and 157 and, therefore, data migration is notparticularly performed.

However, regarding the data which is not mirror-written, processing fordiscarding data in a source controller is required when the LU ownershipis transferred between the different controllers, and if the relevantdata is copied or migrated and is then to be discarded in order toutilize the relevant data. The cache memory 117 is shared by the coresin the controller in order to execute the above-described processing;and the above-described processing is not needed when transferring theLU ownership not between different controllers. Therefore, whether ornot the LU ownership is transferred between different controllersproduces a significant difference in the load. As a result, the type andamount of data in the cache memory are important factors to decide whatkind of LU ownership change to be performed.

The post-LU-ownership-change resource usage change predictioninformation 502 stores a post-LU-ownership-change resource usage changeprediction information table T701 as shown in FIG. 7. Thepost-LU-ownership-change resource usage change prediction informationtable T701 is created by the performance information analysis program216, and the post-LU-ownership-change resource usage change predictioninformation table T701 stores predicted information about what kind ofchanges in the load would occur for each resource after transfer of theLU ownership if the LU ownership in a certain LU is transferred to acertain core.

For example, FIG. 7 shows to what degree the load on each core wouldchange if the LU ownership in LU0 is transferred to each different core.If the LU ownership currently belonging to core 0 for controller 0(destination core “0-0” in FIG. 7) is transferred to core 0 forcontroller 1 (destination core “1-0” in FIG. 7), FIG. 7 shows that loadon the core 0 for controller 0 which originally had the LU ownershipbecomes −7 and load on the core 0 for controller 1 that has taken overthe LU ownership becomes +10.

As in the above-described case, there may be a case where the load onthe entire system will be increased by transfer of the LU ownership.This is because if a host I/O is sent from the host input/output controlunit 119 for the controller 111, the core for the controller 111 needsto receive the command once and then deliver the information to the corein charge of the command, and the processor resources for both cores areslightly consumed.

If the LU ownership is transferred to core 1 for controller 0(destination core “0-1” in FIG. 7), the total amount of change isnegative, which means the load on the entire system will decrease. Thereason for this prediction is also a result of consideration of loadcaused by information communications between the cores. The abovephenomenon occurs when the entire host input/output control unit 119 orthe port that currently mainly receives commands is the hostinput/output control unit or port which the core 1 for controller 0 isin charge of and controls.

If a command is received by the host input/output control unit or portwhich the core 1 for controller 0 is in charge of as described above,information communications between the relevant cores in both states,i.e., in the pre-transfer state where the LU ownership belongs to thecore 0 for controller 0, and in the post-transfer state where the LUownership belongs to the core 0 for controller 1. However, the systemload in the state where the core 0 for controller 0 has the LU ownershipas described above is lower than in the state where the core 0 forcontroller 1 has the LU ownership, because different resources arerequired for the above-mentioned information communications. Exchanginginformation between the cores 0 and 1 for controller 0 is processingcompleted within the memory 116 shared by these cores.

On the other hand, if information is to be delivered from the core 1 forcontroller 0 to the core 0 for controller 1, the information needs topass through the data transfer control unit 112, the inter-controllerbus 182, and the data transfer control unit 152. Therefore, not only thecores, also the bus through which the information passes consume theresources during the processing.

In the case of writing data that may possibly take a long time, forexample, writing data from the core 122 to the memory 156 for theexternal controller, it is common to select a method of reducingresource consumption by the cores by means of post-writing. However, inconsideration of the case where a post-write buffer is already in use,this processing could consume more resources than the memory 116 for thelocal controller.

If exchanging data between the cores in the same controller is comparedto exchanging data between the cores in different controllers asdescribed above, the resource consumption can be reduced in the formercase.

The post-LU-ownership-change resource usage change predictioninformation table T701 stores information in consideration of loadchanges that might occur due to the state changes as described above.Therefore, it is possible to comprehend changes in the systemperformance that might occur due to the transfer of the LU ownership.

The LU ownership change processing overhead prediction information 503stores an LU ownership change processing overhead prediction informationtable T801 as shown in FIG. 8. The LU ownership change processingoverhead prediction information table T801 predicts overhead to begenerated by the transfer processing itself for transferring the LUownership in a certain LU to a core in certain controller. The LUownership change processing overhead prediction information table T801is, unlike other performance information, information about load to begenerated when executing the transfer processing. Therefore, the unituse in this table T801 is, for example, time required for processing.

Regarding the LU ownership change processing, the load, i.e., processingtime varies depending on the amount of transferred data. If the LUownership is transferred from the core 0 for controller 0 (destinationcore “0-0” in FIG. 8) to the core 0 for controller 1 (destination core“1-0” in FIG. 8), and if no data is stored in the cache memory 117,processing for passing the data to the transfer designation isunnecessary.

On the other hand, if data exists in the cache memory 117, theprocessing for passing the data to the transfer designation isnecessary. In this situation, the management information and data existin the local controller area 301. Regarding the management informationand data, from among the management information and data describedabove, that belong only to the local cache memory, for example, originaldata existing in the disks 181, and that do not need to be dualized inthe cache memory, it is necessary to execute processing for discardingsuch management information and data.

If the management information and data exist in the local cache memoryand the external cache memory, the information existing in the localcontroller area 301 needs to be physically and logically migrated to theexternal controller area 341. Similarly on the controller 151 side, themanagement information and data existing in the external controller areain the cache memory 157 need to be physically and logically migrated tothe local controller area.

Next, a processing sequence for load distribution processing will beexplained with reference to the flowchart in FIG. 9. The followingprocessing is executed by the core 122 or 162 according to the relevantprograms. First, an evaluation function is decided using the informationin the balancing parameter information table T402 in accordance with theperformance information analysis program 216 (S901). As a result, whichitem should be prioritized is decided regarding, for example, the loadbalance and the system performance.

Next, the performance information 222 is obtained by the performanceinformation measurement program 215, and this information is analyzed bythe performance information analysis program 216 (S902). The performanceinformation acquisition results are written to the resource usagemanagement information table T601, and the performance informationanalysis results are written to the post-LU-ownership-change resourceusage change prediction information table T701 and the LU ownershipchange processing overhead prediction information table T801.

Subsequently, whether simplified balancing processing is possible or notis judged (S903). The simplified balancing processing is relativelysimple processing for deciding the details of the LU ownership changeprocessing and for executing the transfer as described later. In thisprocessing, processing for deciding the transfer source and the transferdestination is first performed. Therefore, as applicable conditions inthis case, settings are made in the balancing parameter informationtable T402 so that the load balance is prioritized and the systemperformance is not prioritized so much.

If S903 returns an affirmative judgment (the simplified balancingprocessing is possible), the simplified balancing processing is executed(S904). If S903 returns a negative judgment, normal balancing processingis executed (S905).

Next, the performance information acquisition and analysis processing(S902) will be explained with reference to FIG. 14. The followingprocessing is executed by the core 122 or 162 according to the relevantprograms. First, the usage of each resource is measured by theperformance information measurement program 215 (S1401). Since theperformance information acquired in this step is used for judgment inthe LU ownership change processing, not only a simple resource usagerate, but also further detailed information are required. For example,regarding the CPU usage rate of a certain core, the usage rate of eachmanagement unit, not the simple usage rate of the entire core, ismeasured. Since the management unit is an “LU” in this embodiment, theusage rate of each LU for each core is measured. The same applies toother resources.

Information used for judgment of the status after the LU ownershipchange is also necessary. In addition to the above-described informationindicating which LU is used to what degree, information relating to theusage rate of the inter-controller bus 182 include: informationindicating that the usage rate the inter-controller bus 182 has changeddue to mirror-writing of write data from the host; informationindicating that the usage rate of the inter-controller bus 182 haschanged due to transfer of read data from the disk 181 to the othercontroller; or information indicating the usage rate of the former caseand the usage rate of the latter case.

In the case of mirror-writing of write data, load changes will not occurbefore and after transfer of the LU ownership even if the LU ownershipis transferred between the different controllers. However, in the caseof, for example, read data transfer, whether it is necessary to use theinter-controller bus 182 or not changes depending on whether the diskinput/output control unit 118 or 158 and the host input/output controlunit 119 or 159 used when reading data from the disk 181 are in the samecontroller or not. The usage of the internal buses such as the bus 132is also measured for each type of data transfer because of the samereason as described above.

Next, the measured resource usage is output to the resource usagemanagement information table T601 (S1402). Although the resource usagemanagement information table T601 stores only the representativeinformation, the aforementioned information such as the usage rates ofdifferent types of data transfer is also output to the resource usagemanagement information table T601.

Subsequently, LU ownership change patterns are extracted (S1411). Inthis step, all the possible LU ownership change patterns are extractedfor each management unit. For example, as shown in the LU ownershipmanagement information table T401, the LU ownership in LU0 is assignedto the CPU core with the controller number “0” and the core number “0”;and in a system having two CPU cores for each controller, LU ownershipchange destination candidates for LU0 are (0-1), (1-0), and (1-1).

Incidentally, numbers in parentheses indicates “controller number-corenumber.” The above-mentioned candidates may be further narrowed downdepending on LU ownership change settings described later in detail.Furthermore, there may be a case where the LU ownership cannot betransferred due to occurrence of a failure in hardware or software; andalso in this case, besides the settings made by an administrator, theaforementioned LU ownership change destination candidates will benarrowed down.

Subsequently, whether analysis of all the LU ownership change patternsis completed or not is judged (S1412). In this step, whether or not theanalysis processing (S1422 and S1423) described later is completed forall the LU ownership change patterns extracted in S1411 is judged; andif S1412 returns an affirmative judgment (the analysis of all the LUownership change patterns is completed), output processing (S1431) isexecuted; or if S1412 returns a negative judgment (the analysis of allthe LU ownership change patterns is not completed), the LU ownershipchange pattern selection (S1421) is executed.

In the LU ownership pattern selection processing S1421, an LU ownershipchange pattern for which S1422 and S1423 have not been performed issearched for from among the LU ownership change patterns extracted inS1411, and such an LU ownership change pattern is selected as the objectof the following processing.

Next, how the resource usage will change after the LU ownership changeis predicted for the LU ownership change pattern selected in S1421(S1422). In the following explanation, in a case where, for example, theLU ownership in LU0 assigned to the core 0 for controller 0 istransferred to the core 1 for controller 0 and to the core 0 forcontroller 1 respectively, how to predict changes that might occur dueto the LU ownership change will be described with reference to thepost-LU-ownership-change resource usage change prediction informationtable T701.

First, information about the resources that LU0 is currently using isoutput to the resource usage management information table T601 in S1411.An arbitrary unit can be used for the usage rate of each resource in theresource usage management information table T601 and, for example, “%”is used as the unit.

In this example shown in the resource usage management information tableT601, LU0 uses 10% of the CPU core resource of the core 0 for controller0 and 2% of the CPU core resource of the core 1 for controller 0. Thereason why LU0 uses 2% of the CPU core resource of the core 1 forcontroller 0 in which LU0 does not have the LU ownership is because theconfiguration where the core 1 for controller 0 controls the diskinput/output control unit 118 is assumed.

As a matter of course, if the above-described assumption is applied to aconfiguration where the core 0 for controller 0 and the core 1 forcontroller 0 can respectively freely use all the resources of the diskinput/output control unit 118, communications between the cores andinter-core association processing will be enhanced.

However, if only a single core can be used in a function of the diskinput/output control unit 118, or if the disk input/output control unit118 has two or more independent resources and each core occupies anduses these resources in order to reduce overhead, for example, for thepurpose of exclusive control, the configuration in which each coreoccupies part of the resources of the disk input/output control unit 118as described above is also possible.

The usage rate of the inter-controller bus is 0%, that is, theinter-controller bus is not used. This means that data which needs to bemirror-written is not exchanged with regard to LU0.

As changes after the LU ownership in LU0 is transferred to the core 1for controller 0, the resource usage change prediction information tableT701 show “−8%” for the core 0 for controller 0 and “+6%” for the core 1for controller 0. In other words, the post-transfer usage rate of thecore 0 for controller 0 is 2%.

This is because when receiving an input/output request issued from thehost computer 103 in this embodiment, the core 0 for controller 0executes processing for analyzing the received request once and usingthe processor resources for this analysis processing is assumed.Needless to say, a configuration in which the physical port thatreceived the request in the host input/output control unit 119 assignsthe analysis to a core, and a configuration in which at the time ofreception of the request, the received request analysis processing isassigned by the function of the host input/output control unit 119 to anappropriate core, that is, the core having the LU ownership or the corewith a low resource usage rate at that time are also possible.Particularly in the latter configuration, there may be a case where theCPU usage rate of the core 0 for controller 0 becomes “0.”

In this embodiment, a configuration in which part of the resources ofthe host input/output control unit 119 is occupied by the respectivecores is assumed in the same manner as in the processing for assigningthe core to the disk input/output control unit 118 as described above.Since the core 1 for controller 0 newly takes charge of the processingwhich has been executed by the core 0 for controller 0 which had the LUownership before, the CPU usage rate of the core 1 for controller 0increases, which results in 6%. When attention is focused on a total ofthe CPU usage rates, the total usage rate before the transfer is 12% andthe total usage rate after the transfer is 10%, so that the total usagerates before and after the transfer are not the same.

This means that based on the above-described assumption that the core 1for controller 0 uses the disk input/output control unit 118, processingfor communications between the controller 0 core 0 and the core 1 forcontroller 0 that may occur when the core 0 for controller 0 has the LUownership at the time of issuance of an input/output request to the disk181 becomes no longer necessary and, therefore, the total usage rate ofboth the cores reduces. On the other hand, the usage rate of thecontroller bus remains to be “0” because the LU ownership is transferrednot between the different controllers and it is thereby unnecessary totransfer data.

As for a change after transferring the LU ownership in LU0 to the core 0for controller 1, the usage rate of the core 0 for controller 0 is −7%and the usage rate of the core 0 for controller 1 is +10%. The resourceusage rate of the core 0 for controller 0 does not become 0% because ofthe same reason as in the aforementioned case of transfer of the LUownership to the core 1 for controller 0. Also, this transfer processingis processing for transferring the LU ownership between the differentcontrollers and the resource usage rate of the inter-controller bus isalso predicted to increase by +5%.

This is because the configuration in which the core having the LUownership uses the disk input/output control unit for the localcontroller and the cache memory for the local controller is assumed inthis embodiment. Therefore, it is necessary to use the inter-controllerbus 182 in order to exchange data using the host input/output controlunit 119 for the controller 111 that actually received the input/outputrequest from the host computer 103, which results in an increase of thisresource usage rate.

It is also possible to not use the aforementioned configuration, andselect a configuration in which the inter-controller bus 182 is not usedby using only the resources of the external controller. Specificallyspeaking, this is the configuration in which the core 0 for controller 1controls the disk input/output control unit 118 for the controller 111and exchanges data using the cache memory 117. In this case, no changeis predicted in the usage of the inter-controller bus 182.

As described above, changes in the processor usage rates and the usagerate of the inter-controller bus 182 after the LU ownership change arepredicted. Changes after the LU ownership change are also predicted withregard to other resources in the same manner.

Next, overhead to be generated by the transfer processing itself whenexecuting the LU ownership change processing for the LU ownership changepattern selected in S1421 is predicted (S1423).

There are two types of LU ownership change processing: managementinformation transfer and data transfer. The management informationtransfer is processing for transferring information, which is used toexecute processing relating to a certain management unit (LU0 in theexample used in S1422), from a certain CPU core (the core 0 forcontroller 0 in the above-mentioned example) to be placed under thecontrol of an LU ownership change destination candidate (the core 1 forcontroller 0 or the core 0 for controller 1 in the above-mentionedexample). Whether or not data copying is conducted from the memory 116to the memory 116 or the memory 156 during the above transfer processingdepends on the implementation.

The same can be said for the case where the management information is inthe cache memory. “Data” in the data transfer means data which exists inthe cache memory and is exchanged with the host computer 103 or 104.This data is read from the disk 181 or needs to be written. Regardingthe read data, it can be recovered by reading it from the disk 181 againwhenever necessary, so that it is possible to discard this data, thatis, to discard management information of that data when transferring themanagement information as described above. Also regarding this datatransfer, whether or not data copying is conducted from the cache memory117 to the cache memory 157 depends on the implementation as in the caseof the management information.

In the LU ownership change processing overhead prediction informationtable T801, the usage rate of the inter-controller bus is predicted toincrease based on the premise that the inter-controller bus 182 is usedfor data transfer.

Incidentally, unlike the resource usage management information 501 orthe post-LU-ownership-change resource usage change predictioninformation 502, the LU ownership change processing overhead predictioninformation 503 shows the overhead to be generated when executingcertain processing (LU ownership change processing) and, therefore, usesa different unit for numeric values. For example, the numeric values areindicated as the usage rates of the respective resources, assuming thatthe LU ownership change processing is executed in one second. When thenumeric values are expressed in this manner, and if the usage rateexceeds 100%, it is possible to determine that the transfer in onesecond is impossible.

After completion of S1423, the processing returns to the processing forjudging whether or not the analysis of all the LU ownership changepatters is completed (S1412).

If it is determined in S1412 that the processing for analyzing all theLU ownership change patterns extracted in S1411 (S1421, S1422, S1423) iscompleted, the post-LU-ownership-change resource usage change predictioninformation 502 and the LU ownership change processing overheadprediction information 503 are output (S1431).

Next, the simplified balancing processing (S904) will be explained withreference to the flowchart in FIG. 10. The following processing isexecuted by the core 122 or 162 according to the relevant programs.First, all the cores in the storage system 101 are registered astransfer source core candidates (S1001). Next, all the cores in thestorage system 101 are registered as transfer destination corecandidates (S1002). Subsequently, the core with the highest load isselected as the transfer source core from among the transfer sourcecandidates (S1003). Then, the core with the lowest load is selected asthe transfer destination core from among the transfer destinationcandidates (S1004).

In order to transfer one or more LUs from the selected transfer sourcecore to the selected transfer destination core, whether any suitable LUin terms of load balance exists or not is judged (S1005). As an exampleof the case where there is no suitable LU, there may be a case where thecore with high load is in charge of only one LU.

In this case, the load on that LU is extremely high and it can bepredicted that load imbalance will occur to whichever core the LUownership is transferred. Therefore, the above-described case is notideal for the transfer. As another example of the case where there is nosuitable LU, there may be a case where only LUs whose transfer isprohibited in the balancing parameter information table T402 or forwhich quasi prohibition settings are made in the balancing parameterinformation table T402 exist.

If one or more LUs suitable for transfer exist in S1005, the LUownership in the relevant LU(s) is transferred from the currentlyselected transfer source core to the transfer destination core (S1006),thereby completing the simplified balancing processing.

If S1005 returns a negative judgment (there is no LU suitable fortransfer), whether any other transfer destination core candidate existsor not is judged (S1011). If another transfer destination core candidateexists, the core currently selected as the transfer destination core isfirst removed from the transfer destination candidates (S1012) and theprocessing continues from S1004. If no other transfer destinationcandidate exists in S1011, whether any other transfer source candidatecore exists or not is then judged (S1013).

If S1013 returns an affirmative judgment (another transfer sourcecandidate core exists), the core currently selected as the transfersource core is removed from the transfer source candidates (S1014), andthen the processing returns to S1002. If S1013 returns a negativejudgment (no transfer source candidate exists other than the currentlyselected core), this means that LUs suitable for transfer do not existwith regard to all the combinations of the transfer source cores and thetransfer destination cores and, therefore, the simplified balancingprocessing terminates.

Incidentally, there is a more simplified judgment method of, instead ofthe processing from S1001 to S1004, selecting a core with the maximumload as the transfer source core and a core with the minimum load as thetransfer destination core and starting the processing in the state wherethere is no other candidate. Since the core with the maximum load andthe core with the minimum load are always selected as candidates for theLU ownership change, it is possible to judge the necessity of executingthe load balancing easily and under low load.

Next, the normal balancing processing will be explained with referenceto the flowchart in FIG. 11. The following processing is executed by thecore 122 or 162 according to the relevant programs. First, the transfersource core, the transfer destination core, and the transfer object(s)LU(s) are respectively selected from the patterns which have not beenselected (S1101). Next, the selected conditions are evaluated using theevaluation function (S1102).

This evaluation function is the function set in S901 and which entryshould be prioritized is reflected in the evaluation function accordingto the settings made by the user. Subsequently, whether or not anypattern that has not been selected exists is judged (S1103). If there isany pattern that has not been selected, the processing returns to S1101.

In other words, S1102 is executed for all the patterns. If there is nomore pattern that has not been selected in S1103, the LU ownershipchange processing is executed based on the pattern with the bestevaluation result from among the obtained evaluation results (S1104).

By the method described above, the optimum transfer processing can berealized in accordance with the user's settings and aim including theresource usage which changes after the transfer, load changes caused bythe LU ownership change between the different controllers, and theoverhead to be generated by the transfer processing itself.

Next, a management screen to which the user's instruction on the loadbalance is input will be explained with reference to FIG. 12. Amanagement screen 1201 is a screen displayed on the management host 105to set with what priorities the respective items should be evaluatedwhen balancing the load, and the management screen 1201 is constitutedfrom an automatic transfer setting section 1202, an LU-based automatictransfer setting section 1203, an “OK” button 1204, and a “Cancel”button 1205.

The automatic transfer setting section 1202 has an automatic transfersetting parameter table T1212. The automatic transfer setting parametertable T1212 is used to set whether the automatic transfer processingitself is possible or not, the performance balance, and the respectivepriorities for the performance of the entire storage system.Furthermore, the setting to specify to what degree the transfer overheadshould be prioritized when transferring the LU ownership, andinformation about to what degree reference should be made to the pastperformance history as the reference range of performance information tobe used when judging the transfer of the LU ownership.

The LU-based automatic transfer setting 1203 has an LU-based automatictransfer setting table T1203. The LU-based automatic transfer settingtable T1203 is constituted from, for each LU which is the unit formanaging the LU ownership in this embodiment: information about whichcontroller and core are currently in charge of the relevant LU; settingsmade by the user to specify to which core the relevant LU should beassigned; and settings to specify whether the relevant LU should be theobject of the automatic transfer, and to what degree of priority shouldbe set if the relevant LU is the object of the automatic transfer.

The “OK” button 1204 and the “Cancel” button 1205 are buttons fordetermining whether the settings in the management screen 1201 are to bevalidated or discarded.

Next, another method of inputting the user's instruction on the loadbalance will be explained with reference to FIG. 17 showing a managementscreen. A management screen 1701 is a screen used to set the prioritiesfor load balancing processing by means of a certain level of automaticsetting. The management screen 1701 is constituted from an automaticsetting section 1702, an “OK” button 1703, and a “Cancel” button 1704.

In the automatic setting section 1702, there are a radio button 1711 forvalidating the automatic setting and a radio button 1712 for nullifyingthe automatic setting, and only either one of these buttons 1711 or 1712can be set. Letter strings 1731, 1732 explain the meanings of the radiobuttons 1711, 1712 respectively. If the radio button 1712 is validated,i.e., if the automatic setting is nullified, the user sets parametersfor the load balancing processing as shown in the management screen 1201with a certain level of freedom and in detail.

On the other hand, if the radio button 1711 is validated, i.e., if theautomatic setting is validated, a setting method is further selectedfrom radio buttons 1721, 1722, 1723, and so on. Letter strings 1741,1742, and 1743 explain the meanings of the radio buttons 1721, 1722, and1723, respectively.

If the radio button 1721 is validated, i.e., if the completely automaticsetting is validated, the balancing parameter information 402 which isconstituted from the parameters for the load balancing processing is setcompletely automatically. When this happens, as in the case where thefollowing radio button 1722 or 1723 is set, parameter settings areautomatically selected so that the parameters will be valid for dynamicload changes which are difficult for the use to follow, and for loadchanges having periodical characteristics.

If the radio button 1722 is set, i.e., if the setting to changeparameters according to I/O load is selected, the balancing parameterinformation 402 is set in consideration of the entire I/O load issued tothe storage system 101.

This means that if the I/O load issued to the storage system 101 ishigh, there is a possibility that the storage system 101 may become aperformance bottleneck and, therefore, the balancing parameterinformation 402 is set so that the total performance will be increasedas much as possible as rather than the performance balance. On the otherhand, if the I/O load issued to the storage system 101 is low, thebalancing parameter information 402 is set so that the performancebalance will be prioritized in order to prevent the occurrence of aperformance difference between applications using the storage system 101and prepare for a sudden increase of the I/O load. In other words, thesettings are made to dynamically change the balancing parameterinformation 402 according to the I/O load status of the storage system101.

If the radio button 1723 is set, i.e., if the setting to respond toperiodic load changes on a daily basis is selected, it is assumed that aperiodic load will be issued to the storage system 101 on a daily basis,and periodic changes are recorded and utilized. In other words,characteristics of high load processing such as backups and batchprocessing executed at night are recorded, and the balancing parameterinformation 402 is then dynamically changed so that it can promptlyfollow the recorded characteristics.

The “OK” button 1703 and the “Cancel” button 1704 are buttons fordetermining whether the settings in the management screen 1701 are to bevalidated or discarded.

Next, a screen used to inform the user of internal performanceinformation about the storage system 101 will be explained withreference to FIG. 15. The internal performance information isconstituted from resource usage 1511, resource usage change prediction1521, LU ownership change processing overhead prediction 1531, an “OK”button 1541, and an “Update” button 1542 on the management screen 1501.

The resource usage 1511 displays the present resource usage and the pastresource usage in the form of a resource usage table T1512. Theinformation displayed in this table is the same as that shown in theresource usage management information table T601. Needless to say, otherrepresentation methods such as graphic representation are also possibleso that the user can easily and visually comprehend the status.

The resource usage change prediction 1521 is constituted from a resourceusage change prediction table T1522. The information displayed in thistable is the same as that shown in the post-LU-ownership-change resourceusage change prediction information table T701. As in the case of T1512,this table can employ the same representation as that of the resourceusage 1511 in order to indicate the usage after the LU ownership changeso that the user can easily comprehend the status. Furthermore, the formin which the past resource usage change prediction history isadditionally displayed is also possible.

The LU ownership change processing overhead prediction 1531 isconstituted from an LU ownership change processing overhead predictiontable T1532. The information displayed in this table is the same as thatshown in the LU ownership change processing overhead predictioninformation table T801. As in the case of T1512, the representation ofthis table can be changed to indicate, for example, time for thetransfer processing using all the resources so that the user can easilycomprehend the status.

The “OK” button 1541 is a button for terminating the display processing.The “Update” button 1542 is a button for updating the displayedinformation.

Next, a screen used to inform the user of the LU ownership changeprocessing history will be explained with reference to FIG. 16. The LUownership change processing history information is constituted from anLU ownership change processing execution history 1611, an “OK” button1621, and an “Update” button 1622 on the management screen 1601.

The LU ownership change processing execution history 1611 is constitutedfrom an LU ownership change processing execution history table T1612.The LU ownership change processing execution history table T1612 isconstituted from time of execution of the LU ownership change processingin the past, an object LU, pre-transfer CPU core, and a post-transferCPU core. The LU ownership change processing execution history tableT1612 can inform the user of how the LU ownership change processing hasbeen executed, and the user can check if the transfer has been conductedexactly how it was originally intended in the settings of FIG. 12.

The “OK” button 1621 is a button for terminating the display processing.The “Update” button 1622 is a button for updating the displayed historyinformation.

When distributing the load on the respective asymmetric cores 122, 162that receive an LU ownership in LU(s) and take charge of processing theLU(s) according to this embodiment, the core having the LU ownershipextracts, for each LU based on the LU ownership management informationT401, patterns showing the relationship between the core having the LUownership and the transfer destination candidate core; measures, foreach LU, the usage of a plurality of resources constituting the storagesystem 101; predicts, for each LU based on the measurement results,changes in the usage of the plurality of resources that might occurafter the transfer of the LU ownership; also predicts, for each LU basedon the measurement results, overhead to be generated by the LU ownershipchange processing itself; selects, from among the respective extractedpatterns based on the respective prediction results, a pattern thatmatches the setting information (balancing parameter information 402);and transfers the LU ownership to the core belonging to the selectedpattern.

INDUSTRIAL APPLICABILITY

According to this embodiment, it is possible to carry out optimum loaddistribution to a plurality of asymmetric cores in accordance withsettings.

1. A storage system comprising; a plurality of storage devices, whereina plurality of logical units (LU) is configured in physical storageareas of the storage devices; and a plurality of controllers connectedto each other via a bus, in which each of the controllers includes aplurality of processing cores in charge of input/output processing ofinput/output to/from the plurality of logical units (LU); wherein eachprocessing core is configured to be in charge of input/output processingof input/output to/from a respective logical unit, to set the respectivelogical unit as an access object for a host computer and to controlsending/receiving of data to/from one or more storage devices inassociation with read/write from/to the respective logical unit; andwherein each of the controllers is configured to: (a) extract, for eachof the logical units, a plurality of possible LU ownership changepatterns based on LU ownership management information, which definescorrespondence relationships between the logical units and theprocessing cores having LU ownerships for the logical units,respectively, in that the correspondence relationships indicate whichprocessing core is currently in charge of processing with regard to eachlogical unit, wherein each possible LU ownership change patternindicates a combination of the processing core, which is currently incharge of the respective logical unit, as an LU ownership transfersource and another processing core as an LU ownership transferdestination candidate to which an LU ownership for the respectivelogical unit can be transferred by means of an LU ownership transfer;(b) measure, for each of the logical units, the usage of resources inthe data processing for the logical unit, wherein the resources includethe plurality of processing cores and other resources constituting thecontrollers; (c) predict, for each of the logical units and eachpossible LU ownership change pattern for the respective logical unit, achange in the usage of the resources, including the respective LUownership transfer destination candidate core of the respective possibleLU ownership change pattern, after LU ownership transfer from therespective LU ownership transfer source core to the respective LUownership transfer destination candidate core based on the measurementresults in (b); (d) predict, for each of the logical units and eachpossible LU ownership change pattern for the respective logical unit, arespective overhead corresponding to a load to be generated whenexecuting transfer processing in the LU ownership transfer from therespective LU ownership transfer source core to the respective LUownership transfer destination candidate core; and (e) select one of theplurality of extracted LU ownership change patterns which matchessetting information including one or more policies a user sets for loadbalance based on the respective prediction results of the predictions in(c) and (d); and (f) execute the LU ownership transfer from therespective LU ownership transfer source core to the respective LUownership transfer destination candidate core belonging to the selectedLU ownership change pattern; and (g) register the selected LU ownershipchange pattern in the LU ownership management information; wherein thecontrollers are configured to execute the LU ownership transfer in (f)between cores existing in different controllers are well as betweencores existing in the same controller; and wherein the LU ownershipchange pattern corresponding to the LU ownership transfer between thecontrollers is included in the possible LU ownership change patterns forwhich the prediction of change in the usage of the resources isperformed.